1. Field of the Invention
The present invention relates to an apparatus for measuring the static parameters of integrated circuits, and in particular, to an apparatus for measuring the static parameters of integrated circuits that automatically determines the output mode according to the load of the integrated circuits.
2. Description of the Related Art
The testing of integrated circuits usually includes electrical testing and functional testing of the integrated circuit. The electrical testing of the integrated circuit has to test the static parameters, including direct operation voltage testing, direct operation current, and leakage current, etc.
Please refer to FIG. 1, which shows a circuit diagram of an apparatus for measuring the static parameters of integrated circuits of the prior art. The measuring apparatus 1 is used for testing the static parameters of a tested integrated circuit 2. The measuring apparatus 1 includes a main control unit 10, an analog switch 12, a current sampling unit 14, a voltage-sampling unit 16 and a level-clamping protection unit 18. The main control unit 10 includes a capacitor C2, an operation amplifier OPA1, and a plurality of resistors R3, R4 and R5.
When the measuring apparatus 1 of the prior art is used for testing the tested integrated circuit 2, an output mode of the testing needs to be determined in advance. The output mode includes a voltage output mode and a current output mode. In FIG. 1, during operation in voltage output mode, an output voltage needs to be inputted into the main control unit 10. The main control unit 10 provides a voltage-testing signal to the tested integrated circuit 2 according to the output voltage. The voltage-sampling unit 16 obtains the voltage of the tested integrated circuit 2 and outputs a feedback voltage signal v_signal. The feedback voltage signal v_signal is fed back to the main control unit 10 via the analog switch 12. The current sampling unit 14 obtains the current flowing through the tested integrated circuit 2 via a programmable resistor 15 and outputs a feedback current signal i_signal.
In the voltage output mode, the main control unit 10 provides the voltage-testing signal to the tested integrated circuit 2, and achieves a stable negative feedback via the voltage feedback method. If the current flowing through the tested integrated circuit 2 is normal, the level-clamping protection unit 18 separates the feedback current signal i_signal from feeding back to the main control unit 10. If the current flowing through the tested integrated circuit 2 is abnormal, the level-clamping protection unit 18 outputs an inverse voltage that is bigger than the output voltage to the main control unit 10 to protect the measuring apparatus 1. Furthermore, the tester can obtain the operation current of the tested integrated circuit 2 according to the feedback current signal i_signal.
During operation in current output mode, the output current needs to be inputted into the main control unit 10. The main control unit 10 provides a current testing signal to the tested integrated circuit 2 according to the output current. The current sampling unit 14 obtains the current flowing through the tested integrated circuit 2 and outputs a feedback current signal i_signal. The feedback current signal i_signal is fed back to the main control unit 10 via the analog switch 12. The voltage-sampling unit 16 obtains the voltage of the tested integrated circuit 2 and outputs a feedback voltage signal v_signal.
In the current output mode, the main control unit 10 provides the current testing signal to the tested integrated circuit 2, and achieves a stable negative feedback via the current feedback method. Meanwhile, if the voltage of the tested integrated circuit 2 is normal, the level-clamping protection unit 18 prevents the feedback voltage signal v_signal from feeding back to the main control unit 10. If the voltage of the tested integrated circuit 2 is abnormal, the level-clamping protection unit 18 outputs an inverse current that is bigger than the output current to the main control unit 10 to protect the measuring apparatus 1. Furthermore, the tester can obtain the operation voltage of the tested integrated circuit 2 according to the feedback voltage signal v_signal.
The measuring apparatus 1 of the prior art uses the level-clamping protection unit 18 to protect the measuring apparatus 1. However, the level-clamping protection unit 18 generates an inverse voltage whose magnitude is larger than the operation voltage. The inverse voltage or current will damage the tested integrated circuit 2, and an unstable oscillation voltage is also generated and the operation condition will be misjudged.
FIG. 2 shows a waveform diagram of the operation current I of the measuring apparatus of the prior art operated at voltage output mode. When the measuring apparatus 1 is operated at voltage output mode, the operation current Im of the tested integrated circuit 2 has the ripple or oscillation waveform due to the operation of the level-clamping protection unit 18.